1. Technical Field
The present disclosure relates to a wireless charging system, and more particularly, to a wireless charging system capable of preventing output and power transmission efficiency from being suddenly reduced even though a deviation between a transmitting coil and a receiving coil occurs.
2. Description of the Related Art
Recently, technology surrounding plug-in hybrid vehicles and electric vehicles has rapidly developed. In hybrid or electric vehicles, some or all of driving force is electric energy. In order to charge electric energy, methods for putting a wired plug connected to a charger in an outlet and for wirelessly charging electric energy have been used.
The method for wirelessly charging electric energy can be classified into two types: electromagnetic induction and resonance. In the case of the electromagnetic induction charging, a power transmittable distance between the transmitting coil (buried in a parking space, for example) and the receiving coil (equipped in the vehicle, for example) is very short. Therefore, resonance charging has been adopted to secure a power transmission length longer than that of electromagnetic induction charging.
Problematically, when there is no accurate matching between the transmitting coil and the receiving coil, output and charging efficiency may be suddenly reduced. To solve this problem, a method for increasing a size of the transmitting coil and the receiving coil has been proposed but may suddenly increase electromagnetic wave emissions.
FIGS. 1A and 1B are diagrams illustrating a structure of a transmitting coil and the receiving coil according to the related art and a direction of magnetic field in the structure. Both of the transmitting coil and the receiving coil have a circular shape, and a tolerance in an x-direction and a y-direction between the coils relies on a diameter of each coil. Theoretically, when deviations in the x-direction and the y-direction of the transmitting coil and the receiving coil occur due to a diameter of a coil, the output is reduced to 0. When a diameter of the coils is increased, the structure of the transmitting coil and the receiving coil is insensitive to the deviations in the x-direction and the y-direction of the coils, but has the increased size and material costs and the increased electromagnetic wave emissions to the surroundings, thereby making it difficult to satisfy an electromagnetic wave standard.
FIGS. 2A and 2B are diagrams schematically illustrating a wireless charging system having a solenoid type coil structure. The tolerance in the y-direction of the transmitting coil and the receiving coil relies on a width Wo of a core of the receiving coil. However, the tolerance in the x-direction is larger than that in the y-direction. That is, the transmitting and receiving coils illustrated in FIGS. 2A and 2B embodies a slightly improved tolerance in the x-direction over the circular transmitting and receiving coils illustrated in FIGS. 1A and 1B. Further, in the coils having the form as illustrated in FIGS. 2A and 2B, a magnetic field is generated in front of and in back of the vehicle, and therefore, the electromagnetic wave emissions generated at both sides of the vehicle may also be reduced.
However, when a deviation in the y-direction still occurs, the output and power transmission efficiency may be reduced. Therefore, there is a need to develop a wireless charging system capable of preventing the output and power transmission efficiency from being suddenly reduced even though the transmitting coil and the receiving coil are positioned to deviate from each other.